c. Secondary VJaves . Along the length of the tank, between the 

 generator and the toe of the profile, wave heights on any given recording 

 varied as a result of secondary waves. Galvin (1972) and Hulsbergen 

 (1974) described secondary waves (called solitons by Galvin) and their 

 effects; secondary waves can be observed on the wave records. The wave 

 height variability due to secondary waves does not affect the incident 

 and reflected wave heights reported here since the incident and reflected 

 wave heights are spatial averages. 



2. Profile Equilibrium . 



Experiment 72D-06 was the third effort in an attempt to define the 

 equilibrium profile shape for this set of wave and sediment conditions. 

 Based on experience gained from experiments 70X-06 and 71Y-06 (see Vols. 

 11 and III), the initial slope of 0.05 selected for this experiment was 

 thought to be much closer t^o the equilibrium profile, and was certainly 

 close to the final profile in experiment 71Y-06; e.g., erosion of the 

 longshore bar and development of the long, flat shelf in the inshore 

 zone that occurred after 200 hours in experiment 71Y-06 occurred after 

 only 3 hours in this experiment. Also, at 100 hours in this experiment 

 the inshore zone had the same length as at 375 hours in experiment 71Y-06, 

 but the offshore zone was not nearly as steep and extended farther toward 

 the wave generator. 



After 125 hours in this experiment the shoreline stopped retreating, and 

 after 135 hours the shoreline stabilized, which never occurred in experi- 

 ment 71Y-06. Even though the shoreline stabilized, the profile con- 

 tinued to change. A large trough was scoured near the shoreward edge of 

 the inshore zone and the material was deposited in the offshore zone. 

 The offshore slope was never as steep in experiment 72D-06 as it was in 

 experiment 71Y-06. 



Although the flatter initial slope hastened the profile development 

 and during the last 80 hours the water temperature was fairly constant 

 (below 10° Celsius), the profile never reached equilibrium. 



3. Other Laboratory Effects . 



Chesnutt (1975) compared the profile development in this experiment 

 with that in experiment 71Y-06 and discussed the effect of initial slope. 



As discussed in Section IV, 2, the flatter initial slope hastened the 

 development of the typical foreshore and inshore shapes for this set of 

 wave and sediment conditions (Fig. 8 in this report; Fig. 9 in Vol. III). 

 However, three striking differences between the final profile in experi- 

 ment 72D-06 and the final profile in experiment 71Y-06 were: (a) A stable 

 foreshore and shoreline, (b) a large trough at the shoreward edge of the 

 inshore zone, and (c) a longer and less steep offshore zone. The longer 

 offshore zone, resulting directly from the flatter initial slope, may be 

 the cause for the other differences. First, the wave traveling over the 

 0.05 slope was subject to greater energy losses due to bottom friction, 

 particularly after the inshore zone became wider, and as a result the 



51 



